1. Field of the Invention
The present invention relates to an electroconductive layer which is to be bonded to a resin layer, a laminate using this layer, and producing processes thereof.
2. Description of Related Art
Ordinary multilayer wiring boards are each produced by laminating/pressing an inner layer substrate having, on its surface, an electroconductive layer made of copper onto a different inner layer substrate and/or a copper foil with a prepreg interposed therebetween. Their electroconductive layers are connected electrically to each other through a penetrating hole having a hole-wall plated with copper, which is called a through hole. On the electroconductive layer surface of the inner layer substrate, for example, a copper oxide in a needle form, which is called black oxide or brown oxide, may be formed in order to improve the bondability to the prepreg. According to this manner, the needle-form copper oxide penetrates the prepreg to produce an anchor effect. Thus, the bondability is improved.
The copper oxide is excellent in bondability to the prepreg; however, when the copper oxide contacts an acidic solution in a plating step of forming through holes, the oxide is dissolved and discolored to result in a problem that a defect called hallowing is easily caused.
Thus, as a method substituted for the use of black oxide or brown oxide, suggested is a method for forming a tin layer on the surface of a copper layer of an inner layer substrate as disclosed in EP-A1-0 216 531 and JP-A-4-233793. Further, JP-A-1-109796 suggests a method for forming a tin layer on such a copper layer surface, and furthermore subjecting the resultant to treatment with a silane compound in order to improve the bondability of the copper layer to a resin layer. Moreover, JP-A-2000-340948 suggests a method for forming a tin layer on such a copper layer surface in order to improve the bondability of the copper layer to a resin layer similarly, and furthermore suggests a technique for making the copper layer surface rough by etching, thereby expressing an anchor effect. Besides EP-A1-0 216 531, JP-A-2005-23301 and JP-A-2004-349693 suggest a method of forming, on such a copper layer surface, a tin plating treated layer wherein tin, copper and metal(s) other than these are mixed with each other.